The present invention relates to the improvement of the clarity of low density polyethylene film containing anti-block agents. More specifically, the invention relates to the use of polyethylene glycol as an agent to enhance the see-through clarity of low density polyethylene film containing such anti-block agents.
Thin low density polyethylene homopolymer and copolymer and linear low density polyethylene films possess many properties, such as inertness to chemicals, mechanical strength, low moisture vapor permeability, and transparency, which make it desirable as a wrapping and packaging material. However, there is a tendency for adjacent surfaces of such polyethylene film to adhere to one another when subjected to even slight pressure. This phenomenon of thin sheets of film sticking to one another when superimposed is called "blocking" and tends to make the film undesirable for many applications.
It has been known for some time that the "blocking" tendencies of such polyethylene film can be counteracted by the addition of anti-blocking agents to the polymer from which the film is made. Finely divided silica and diatomaceous earth have long been used as anti-blocking agents in polyethylene films. See for example U.S. Pat. Nos. 2,991,264, 3,028,355, and 3,293,206. Polyethylene films which incorporate these materials tend to have a see-through clarity which is unacceptable or at least poor for many commercial applications, especially in the blown film area. These materials do not have as great an effect on the see-through clarity in cast film because cast films inherently have much better see-through clarity than blown films.
It is an object of this invention to provide a method for improving the clarity of polyethylene films, especially blown films, which contain finely divided silica or diatomaceous earth as an anti-blocking agent. Still another object of this invention is to accomplish this improvement in see-through clarity without materially affecting other physical properties of the polyethylene film.